A poly(p-phenylene terephthalamide) fiber (PPTA), an aromatic polyamide fiber which is well-known as Kevlar®available from Du Pont exhibits superior thermal properties and high tensile strength and elastic modulus. These properties are caused by chain stiffness, a high degree of molecular orientation and crystallinity. This fiber is prepared by dry-jet wet spinning a liquid crystalline solution of PPTA in hot 100% sulfuric acid. However, this fiber is readily not dyed and has also a disadvantage of poor adhesion strength due to disadvantages of low compression strength, poor hydrophilicity and high crystallinity.
In an attempt to solve these disadvantages, U.S. Pat. No. 5,073,440 discloses a method in which PPTA and polyvinyl pyrrolidone (PVP) which is a water-soluble polymer are dissolved in 100% sulfuric acid to blend PPTA with PVP, to improve functions such as dyeability, adhesion and hydrophilicity without causing deterioration in mechanical properties. However, Simonutti, et al., investigated miscibility of polymer blends prepared from a PPTA/PVP solution in 100% sulfuric acid by cross-polarization/magic angle spinning solid state 13C NMR spectroscopy. As a result, it can be found that these blends were not homogeneously mixed on a molecular scale, but phase-separated on a scale of a few nanometers, i.e., a nanocomposite (Macromolecules, vol 35, p3563, 2002). That is, according to the technique, crystalline PPTA and non-crystalline PVP polymers are not mixed on a molecular scale, but form a phase-separated nanocomposite. For this reason, composite fibers are non-uniform through heterogeneous mixing, which may disadvantageously cause non-uniform treatment or leveling property defects during dyeing.
In addition, the technique uses strong inorganic acid such as 100% sulfuric acid, thus having several problems such as environmental problems and problems associated with preparation processes. Disadvantageously, sulfuric acid, which is not completely removed in the washing process, may cause problems associated with heterogeneous treatment when applied to functional fibers.
Accordingly, preparation of a molecular miscible blend of crystalline aromatic polyamide and a non-crystalline polymer, a method for uniformly dyeing aromatic polyamide fibers at room pressure, and a method associated with preparation of highly functional aromatic polyamide fibers which may be uniformly dyed have not been suggested to date.